diff --git a/CHANGELOG.md b/CHANGELOG.md
index ce83454dc1..b6c67c1174 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,6 +2,7 @@
 
 ## Features
 
+-   Added `NewmanTobias` li-ion battery model ([#1423](https://github.com/pybamm-team/PyBaMM/pull/1423))
 -   Added `plot_voltage_components` to easily plot the component overpotentials that make up the voltage ([#1419](https://github.com/pybamm-team/PyBaMM/pull/1419))
 -   Made `QuickPlot` more customizable and added an example ([#1419](https://github.com/pybamm-team/PyBaMM/pull/1419))
 -   `Solution` objects can now be created by stepping *different* models ([#1408](https://github.com/pybamm-team/PyBaMM/pull/1408))
diff --git a/pybamm/models/submodels/electrolyte_diffusion/base_electrolyte_diffusion.py b/pybamm/models/submodels/electrolyte_diffusion/base_electrolyte_diffusion.py
index 71712847c3..a2c9ce99d4 100644
--- a/pybamm/models/submodels/electrolyte_diffusion/base_electrolyte_diffusion.py
+++ b/pybamm/models/submodels/electrolyte_diffusion/base_electrolyte_diffusion.py
@@ -134,17 +134,6 @@ def _get_total_concentration_electrolyte(self, c_e, epsilon):
 
         return variables
 
-    def set_boundary_conditions(self, variables):
-
-        c_e = variables["Electrolyte concentration"]
-
-        self.boundary_conditions = {
-            c_e: {
-                "left": (pybamm.Scalar(0), "Neumann"),
-                "right": (pybamm.Scalar(0), "Neumann"),
-            }
-        }
-
     def set_events(self, variables):
         c_e = variables["Electrolyte concentration"]
         self.events.append(
diff --git a/pybamm/models/submodels/electrolyte_diffusion/composite_diffusion.py b/pybamm/models/submodels/electrolyte_diffusion/composite_diffusion.py
index ad37e30b64..ebfa8232fb 100644
--- a/pybamm/models/submodels/electrolyte_diffusion/composite_diffusion.py
+++ b/pybamm/models/submodels/electrolyte_diffusion/composite_diffusion.py
@@ -95,3 +95,14 @@ def set_initial_conditions(self, variables):
         c_e = variables["Electrolyte concentration"]
 
         self.initial_conditions = {c_e: self.param.c_e_init}
+
+    def set_boundary_conditions(self, variables):
+
+        c_e = variables["Electrolyte concentration"]
+
+        self.boundary_conditions = {
+            c_e: {
+                "left": (pybamm.Scalar(0), "Neumann"),
+                "right": (pybamm.Scalar(0), "Neumann"),
+            }
+        }
diff --git a/pybamm/models/submodels/electrolyte_diffusion/constant_concentration.py b/pybamm/models/submodels/electrolyte_diffusion/constant_concentration.py
index 570bce61b3..7001675d2f 100644
--- a/pybamm/models/submodels/electrolyte_diffusion/constant_concentration.py
+++ b/pybamm/models/submodels/electrolyte_diffusion/constant_concentration.py
@@ -45,3 +45,19 @@ def get_coupled_variables(self, variables):
         variables.update(self._get_total_concentration_electrolyte(c_e, eps))
 
         return variables
+
+    def set_boundary_conditions(self, variables):
+        """
+        We provide boundary conditions even though the concentration is constant
+        so that the gradient of the concentration has the correct shape after
+        discretisation.
+        """
+
+        c_e = variables["Electrolyte concentration"]
+
+        self.boundary_conditions = {
+            c_e: {
+                "left": (pybamm.Scalar(0), "Neumann"),
+                "right": (pybamm.Scalar(0), "Neumann"),
+            }
+        }
diff --git a/pybamm/models/submodels/electrolyte_diffusion/full_diffusion.py b/pybamm/models/submodels/electrolyte_diffusion/full_diffusion.py
index 14c09a501b..590f879612 100644
--- a/pybamm/models/submodels/electrolyte_diffusion/full_diffusion.py
+++ b/pybamm/models/submodels/electrolyte_diffusion/full_diffusion.py
@@ -81,3 +81,14 @@ def set_initial_conditions(self, variables):
         c_e = variables["Electrolyte concentration"]
 
         self.initial_conditions = {c_e: self.param.c_e_init}
+
+    def set_boundary_conditions(self, variables):
+
+        c_e = variables["Electrolyte concentration"]
+
+        self.boundary_conditions = {
+            c_e: {
+                "left": (pybamm.Scalar(0), "Neumann"),
+                "right": (pybamm.Scalar(0), "Neumann"),
+            }
+        }